Adaptive Autonomous Robot Teams for Situational Awareness

GRASPUniversity of Pennsylvania

Adaptive Autonomous Robot Teams for Situational Awareness

Georgia Tech’s Role


Personnel

Georgia Tech Faculty

Prof. Ron Arkin Prof. Tucker Balch Dr. Robert Burridge

GRAs Keith O’Hara Patrick Ulam Alan Wagner Matt Powers

Mobile Intelligence Inc. Dr. Doug MacKenzie


Impact – GT Role

• Provide communication-sensitive planning and behavioral control algorithms in support of network-centric warfare, that employ valid communications models provided by BBN

• Provide an integrated mission specification system (MissionLab) spanning heterogeneous teams of UAVs and UGVs

• Demonstrate warfighter-oriented tools in three contexts: simulation, laboratory robots, and in the field


Communication Sensitive Planning • Provide support for terrain models and other

communications relevant topographic features to MissionLab

• Use plans-as-resources as a basis for multiagent robotic communication control (spatial, behavioral, formations, etc.) and integrate within MissionLab


Plans as Resources • Motivated by Payton’s work.

• A precompiled map is an enabling resource.

• Maps converted to a two dimensional gradient mesh a priori using A*.

• Robot queries “internalized plan” for directional “advice” in the form of a vector.

• Queries and advice production are near real-time.


Internalized Plan as Behavior

• The GoToMapVector assemblage controls retrieval of plan vectors from maps, and consists of the following sub-assemblages:

GetMapVector: Retrieves and injects a map vector

Wander: Inject noise Avoid Obstacles MoveToGoal: Only used in experiments of

mixed reactive/planning behavior.


Parallel Internalized Plans• Different internalized

plans can be combined by fusing individual plans.

• Base plan contains only physical objects.

• Other plans contain additional constraints.

• The robot queries advice from the most constrained plan (pessimistic).


Serial Internalized Plans• Different internalized

plans are used one after another.

• Each plan offers situation specific advice.

• Perceptual triggers transition from only plan to another.

• Opportunity for contingency plans.


Initial Results• Additional resources in the

form of internalized plans aids team communication.

• No difference results when

using reactive behaviors vs. communication insensitive plans.

• Communication planning in serial and parallel result in significant improvement in communication.


Plans as Resources: Upcoming work

• Conduct tests on teams of real robots.

• Determine the systems localization and map accuracy requirements.

• Develop techniques for dealing with localization errors and map inaccuracies.

• Extend the planning to 3D and generalize to other space-time dimensions for multi-robot coordination


Communication-sensitive Team Behaviors

• Generation and testing of a new set of reactive communications preserving and recovery behaviors

• Creation of communications recovery and preserving behaviors sensitive to QoS

• Expansion of behaviors in support of line-of-sight and subterranean operations


Communications Recovery Behaviors

• Retrotraverse: Log robot’s position at regular intervals; when comms breaks, move to last N positions logged until comms recovered

• Move to Higher Ground: Use inclinometer data to guide ascent to vantage point for communications recovery

• Nearest Neighbor: Track the last known position of connected robots; if comms lost, move towards the nearest robot’s last position

• Bridging: Couple separated networks by tracking positions and moving towards location of network lesion; currently UAV behavior

• Shepherding: Search out robots that have been cut off from the network; once found, guide back (currently UAV)


Experimental Design

Missions run on simulated Quantico map

20 trials starting at regularly spaced intervals along the western side of the map and moving to a central location on the eastern side of the map

2 UGVs moving in a line formation with 20m spacing

Recovery behaviors used in isolation of one another

Metrics: Mission Completion Rate, Recovery time


Results

Using the Nearest Neighbor Recovery behavior approximately 50% of the trials were finished completely autonomously

Retrotraverse and Move to Higher Ground were usually not able to finish the trials autonomously by themselves and will require transitions/planning once communications recovered

Number of Trials Completed

0

11

0

18

02

8

19

02468

101214161820

Communication Sensitive Behaviors

Tri

als

Co

mp

lete

d

No Preserving, No Recovery

No Preserving, Higher Ground

No Preserving, Nearest Neighbor

No Preserving, Retrotraverse

Maintain Signal Strength, No Recovery

Maintain Signal Strength, Higher Ground

Maintain Signal Strength, Retrotraverse

Maintain Signal Strength, Nearesr Neighbor


Results (2)

Retrotraverse results in the most rapid communications recovery of the behaviors tested.

Move to higher ground results in the slowest recovery rate, largely due to failure when the terrain was level.

Nearest Neighbor was successful in most cases, except in some situations around buildings where the attraction to the lost robot and the repulsion to the building that severed communications causes a local minima

Communications Recovery Time

0

100

200

300

400

500

600

Communications Behaviors

Tim

e

No Preservation, No Recovery

No Preservation, Higher Ground

No Preservation, Retrotraverse

No Preservation, Nearest Neighbor

Maintain Signal Strength, No Recovery

Maintain Signal Strength, Higher Ground

Maintain Signal Strength, Retotraverse

Maintain Signal Strength, Nearest Neighbor


Summary: Communications Recovery

• Retrotraverse provides the most rapid communications recovery Retrotraverse must be augmented with supplementary

behaviors or teleoperation to complete mission

• Move to Higher Ground and Nearest Neighbor perform effectively in many cases There are a number of cases where the behavior will

perform suboptimally Supplementary behaviors or a more complex behavioral

selection may further improve results


Future Work

• Investigate means in which to activate recovery behaviors based on available perceptual features

• Integration of cognizant failure (Gat) for recovery behaviors

• Evaluate performance of recovery behaviors in the context of larger teams, increased formation size, and disparate goals


Communication-Preserving Behaviors with Limited Memory

Value-Based One-Step Look-Ahead Uses predictions of communication quality short

distances from current position to “hill-climb” to better locations with respect to communication

Currently assumes teammates remain still when predicting communication quality to reduce complexity


Communication-Preserving Behaviors

• Operation: Predict communication quality at locations a

small distance away using Map information Network attenuation model Teammates assumed to remain still

Create motion vector based on predicted and current communication quality

Bearing based on predicted quality Magnitude based on current quality



X X

XX

(r = .89)

(r = .85)(r = .74)

(r = .68)

(r = .70)

Predicted communication qualities

Current communication quality

Resulting vector



Without Look-Ahead Behavior:

Obstacle-splitting endangers communication quality



With Look-Ahead Behavior:

Obstacle-splitting phenomena eliminated


Communication-Preserving Behaviors – 1 step

• Future work: Extend behavior to larger groups

Perform quantitative tests Compare to other communication-preserving

behaviors Identify situations where most effective

Integrate into larger scenarios


Memoryless Communication Preserving BehaviorMaintain-Signal-Strength

• Servos on signal strength to preserve communication.

• Sum over every “connected” robot Vector_Magnitude = (T-R)/T when (T-R) > D Vector_Direction = angle to the robot

where T: Target Signal Strength, D: Signal Deadzone, R: Actual Signal strength

• Connected can be defined to mean either directly connected or connected via a multi-hop route.


Illustration of Maintain-Signal-Strength

Communication Quality Decreases

g1 g2

Communication Quality Increases

s1 s2


Communication Preservation Experiments

• Mission: Each robot navigates to its goal. • Team Sizes: 2, 4, 6, and 8 • Distance separating robots: 10, 20, 40 meters • 25 random worlds

12% obstacle coverage 256 x 256 meters

• Three behaviors are compared. No communication behavior (control) MSS using positions of directly connected robots

(single-hop) MSS using all available positions (multi-hop)


Percentage of Time as One Network

• Some communication strategy is needed to keep the network one as you increase the distances or the number of robots.

•There doesn’t seem to be a significant difference between the two variations of the behavior.


Mission Completion Time

• Both variations of the behavior add a significant amount of time to mission completion.


Communication Models and Fidelity

• Working with BBN to incorporate suitable communication models into MissionLab in support of both simulation and field tests


Current Network Model Status• Models wireless communication networks in

3 dimensions.• Integrated into MissionLab • Signal Attenuation

Free-space path-loss Dependent on distance between robots, frequency of

communication band, and antennae height. Line-of-Sight Obstructions

Absolute signal attenuation. Obstructions modeled as arbitrary polygons or right cylinders

with height. Terrain map can be used which can occlude LOS.


The Quantico Overlay From a Communications Perspective


Next Steps in Modeling Network

• Obstructions will attenuate signal at different magnitudes. Model buildings and foliage.

• Accurate model of signal attenuation over rough terrain.

• Mimic capabilities of BBN “black-box”

• Understand how different levels of model fidelity impact multi-robot team performance.


Communication-sensitive Mission Specification

• MissionLab is a usability-tested Mission-specification software developed under extensive DARPA funding (RTPC / UGV Demo II / TMR / UGCV / MARS / FCS-C programs)

• Using MissionLab as a basis: Adapt to incorporate air-ground communication-

sensitive command and control mechanisms Extend to support physical and simulated experiments

for objective air and ground platforms Incorporate new communication tasks and triggers


MissionLab’s Spatial Planner

• Incorporates Navigator Component of the AuRA architecture- A map of obstacles is read in by the system- The map is “grown” to represent configuration space- The free space is partitioned into a collection of convex “meadows” - Start and End points are selected by the user- The planner performs A* search to find an initial path- The path is improved by tautening

• Can be invoked from MissionLab’s cfgedit tool

• Creates an FSA series of waypoints


Initial Map and Meadow Map


Path Chosen and Formation Run


Technology Integration

• Conduct Early-on Demonstrations on Ground Robots at GT

• Provide our Hummer Command and Control Vehicle for Team support at Objective Demonstration


Interface Control Document

• To explicitly capture all aspects of all interconnections between project components. Communications protocols, frequencies, and timing Language and data formats Experimental communications fault injection

• To define new mission description language: CMDL+

• To detail communications-sensitive behaviors developed by project teams. Communication-preserving Communication-recovering


PENNPENN

ROCI

USCHelo

(Mounted in GT Hummer)

ICD

Ref: 2.3.4

BBNICD Ref: 2

.3.7

ICD

Ref: 2.3.8

VIPDispla

y

GaTech

MLab

ICD Ref: 2.3.2

USCPlaye

r

ICD Ref:2.3.1

ICD

Ref

: 2.3

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MLR

PC


GPS Jammer

• Supports evaluation of robot localization methods in challenging environments

• White noise centered on selected frequency

• Power: 50 to 200mw (about 50-100 meters)

• Performance to be characterized in the coming few weeks

Engineered by Daniel Walker (BORG Lab)


Summary - Georgia Tech Contributions• Communications Sensitive Behaviors

Preserving Recovery

• Communications Planning Behaviors Plans as Resources One-step planning Team spatial waypoint planning

• Infrastructure Communications models support MissionLab as an integration vehicle ICD Development lead Hummer base station / Test equipment Scenario development


Backup Slides


Plans in Serial Demo explained

Seven plans are used in this demo

Adaptive Autonomous Robot Teams for Situational Awareness

Documents

Transcript of Adaptive Autonomous Robot Teams for Situational Awareness